Method for synchronizing transducer head scanning motion in sound recording and reproducing machines



Aug. 3, 1965 G. T. STANTON 3,198,527

METHOD FOR SYNCHRONIZING TRANSDUCER HEAD SCANNING MOTION IN SOUND RECORDING AND REPRODUCING MACHINES Original Filed June 8. 1954 4 Sheets-Sheet 1 94 INVENTOR t f 44 40 gem ei 5317102 15' an on Aug. 3, 1965 G. 'r. STANTON METHOD FOR SYNCHRONIZING TRANSDUCER HEAD SCANNING MOTION IN SOUND RECORDING AND REPRODUCING MACHINES ne 8, 1954 4 Sheets-Sheet 2 Original Filed Ju 2/8 INVENTOR /5/ (207a Taylor Stan ton IIIIIIIHHIIHIIIlllllll WIIIHIIHHIIIIHHH 1955 G. T. STANTON 3,198,527

METHOD FOR SYNCHRONIZING TRANSDUCER HEAD SCANNING MOTION IN SOUND RECORDING AND REPRODUGING MACHINES Original Filed June 8, 1954 4 Sheets-Sheet 3 w a o INVENTOR 246 eo giToylorStan on M, M a

ATTORNEYS Aug. 3, 1965 G. T. STANTON METHOD FOR SYNCHRONIZING TRANSDUCER HEAD SCANNING MOTION IN SOUND RECORDING AND REPRODUCING MACHINES Original Filed June 8, 1954 4 Sheets-Sheet 4 l'a'zylorsi'anion M' m4. W

ATTORNEYS United States Patent ice METHOD FOR SYNCI-HKONIZEJG TRANSDUCER HEAD SCANNING MUTIUN IN SQUND P CORDHNG AND REPRODUCING MAE George Taylor Stanton, Fairfield, Conm, assignor to Dictaphone Corporation, Bridgeport, Conn, a corporation of New York Griginal appiication June 8, 1954, Ser. No. 437,762, new Patent No. 2,996,184, dated .June 27, 1961. Divided and this application Sept. 30, 1960, Ser. No. 559,576

5 Claims. (Ql. 274-11) This is a division of application SerialNo. 437,762, filed June 8, 1954, now Patent No. 2,990,184.

This invention relates to sound recording or reproducing machines and to methods and apparatus for producing a synchronization of the scanning relationship of the transducer head relative to the sound tracks in machines using sound records of the type which do not have mechanical grooves, for example, such as magnetic belt records, magnetic disk records, or optical photoelectric records.

The invention has particular utility in machines using belt records, as explained below, but is useful whereever there is a problem of maintaining synchronization of a sound head and a groove-less sound track. In sound recording and reproducing machines using the belt-type of record, various possible arrangements may be provided for supporting and driving the record. For example, in one such machine the record is supported in a loop under tension and passed around a pair of individual rollers. In other machines alternative arrangements may be provided, for example, the belt may be supported by a single expandable rollers, or, if a long length of record is used, the record may be fed into and out of a storage compartment, with only a part of the record being driven at any one time. 7 I

In all of these various types of belt-record machines, the record belt is driven by means of the frictional engagment between the surface of the record and one or more drive rollers or mandrels. It has been found impractical to provide a positive drive relationship between the drive roller and the belt record. The use of sprocket teeth co-operating with sprocket holes in the edges of the belt record, for example, as used with movie film, is impractical because of the excessive wear of the sprocket holes in the record, the weakening of the belt record, and the difiiculty of properly loading and unloading such a record in dictating machines. Unlike a move film in which each individual sprocket hole must engage a sprocket tooth only once during each showing of the film; sound belt record may be revolved hundreds of times during each usage, for the sound track may spiral around the record this many times, and hence each sprocket hole must engage a sprocket tooth once per revolution of the record. Moreover, in the case of magnetic records, they should be adapted for a considerable amount of reuse, making sprocket holes particularly impractical for magnetic belt records. A frictional' drive enables easyloadin'g and unloading'of the 'rnachine and distributes the driving force over the entire surface of the "record, and hence it does not placeany undue wear on any portion of the record.

'Ith'as been found that with this type of frictional drive there is a tendency for the belt to slip 'or creep 'rela tive tothe surface of the drive mandrel or roller, and the extent of this slippage depends upon many variable factors such-as the'humidity, amount of wear present on the roller surface andon the undersurface of-the r cord, etc. Also,'thisslippage may occur in varying amounts both during recording and reproducing. Moreover, the length of'the h elt itself-issubject to change due to stretching 3,198,5 2.? Patented Aug. 3, 1965 under tension, changes in humidity, manufacturing tolerances and age of the record. These various factors add together in cumulative fashion to disturb the rate of motion of the belt record relative to the motion of the drive roller. Thus, under these various conditions, a single rotation of the drive roller may cause a slightly varying percentage of the length of the belt record to be fed past the sound recording or reproducing head. In other words, under various conditions, a different percentageof revolution of the belt record may be produced by a single rotation of the drive roller. This cumulative error in the record travel causes no immediately apparent trouble during sound recording, except that variations in the spacing of the sound tracks may occur as they are formed on the surface of the belt record.

In mechanical recording systems wherein a .stylus physically cuts or embosses a groove or track into the surface of the record, this cumulative errorin the position of the belt record causes no difficulty during sound reproducing, because the reproducing head is mounted with some compliance and the stylus is forced by the walls of the groove on the record surface to follow along in it. However, in other systems of recording, such as magnetic or optical systems, there is no groove to maintain the proper relationship between the reproducing unit and the sound track, and so the reproducing unit may easily get out of phase, i.e. lead or lag to one or the other side of the sound tracks. These phasing difliculties are due both to the original variations and error in spacing of the sound tracks as they were recorded and to the errors in motion of the record itself during reproduction. The methods and'apparatus of the present invention overcome these diiiiculties and may advantageously be used either for recording or reproducing, or for both.

In magnetic sound reproducing machines, when the head shifts into an improper lateral position with respect to the sound track from which sound reproduction is taking place, so that the record-engaging face of the head is partly on and partly oil to one side of the sound track, the reproduced sound signal becomes weak or faded, i.e. the head is partly out of phase with the sound track. If this condition becomes aggravated so that the face of the head lies mid-way between adjacent tracks, or (depending upon the relative widths of the face of the head and of the space between adjacent sound tracks) simultaneously touches or overlaps the adjacent edges of two sound tracks, substantially no sound or (in the overlapping case) intermingled and confused feeble sounds are produced, i.e. the head is completely out of phase with the sound track.

in order to obtain good .quality sound reproduction, it is desirable that the face of the reproducing head never deviate in phase more than a fraction of the width of a single sound track. Even for the lowest quality of reproduction this deviation 'should never exceed more than one-half of the width of a sound track "or should not exceed two-thirds of the spacing :between tracks, whichever isthe lesser distance. That is, the reproducing face of the head should always contact at leastone-half of the width of the soundtrack itself and should not move any closer to the edge of the adjacent track than onethird of the space between adjacent tracks. 1

It is emphasized, as indicatedabovmthat the effects of the creep of the belt record on its drive roller and of changes in the roller or record dimensions are cumulative, and thus after'a relatively few rotations of the drive roller, this error may amount to a considerable length of the belt record; and hence may quickly amount to a large fraction of the width of the sound track, for the sound track follows a more-or-less helical path on the surface of the belt record.

For example, assume that humidity and surface conditions of the record and drive mandrel are such that 0.2% slippage is occurring between them and also assume that due to manufacturing tolerances, temperature, humidity and age the record is 0.3% longer than the designed value. Under these conditions, during each revolution of the record, it drops 0.5% behind its required position. This error is cumulative in effect, and by the end of only 100 revolutions of the record, the head will be completely out of phase with the sound tracks. In fact, after only 50 revolutions, the head is engaging less than one-half of the sound track, which is more than the maximum allowable deviation even for low quality sound reproduction.

Other factors also may contribute to this cumulative error. For example, the diameter of the drive mandrel due to tolerances of temperature variations and wear may be slightly less than the designed value, which has the same efiect as if the circumference of the record is too large. Moreover, in usual ofiice practice a first machine is used for dictation and a second machine is used for transcription. If the diameters of the drive mandrels in these two machines are different, the phasing problem becomes even more acute.

The methods and apparatus of the present invention provide a synchronization between the motion of the surface of the belt record itself and the scanning motion of the transducer unit over the surface of the record. In the described embodiments of the present invention the scanning mechanism repeatedly passes through cycles including two alternate transverse scanning conditions; the transition from the first condition into the second condition is automatic and depends upon the motion of the record drive mechanism. The return change from the second scanning condition into the first scanning condition is caused solely by the relative position of the record itself, which actuates a triggering mechanism. Thus, at the end of each cycle of operation of the synchronizing method, the record and scanning mechanism are placed in synchronism. With this arrangement the scanning of the transducer unit across the surface of the record is at all times controlled or monitored by the motion of the record itself, and hence the scanning relationship is independent of the amount of slippage which may occur and is independent of any changes in record or roller dimensions, or the like, which may take place.

The first and second scanning conditions may occur once during each revolution of the belt record so that synchronization of the scanning is made once per record revolution. Or they may occur more than once per revolution of the record, or only after predetermined integral numbers of record revolutions, or at random, as will be understood from the detailed description of the various embodiments of my invention disclosed herein. But in every case the scanning motion of the transducer head is controlled or monitored by the motion of the record surface itself and is independent of the various factors discussed above.

In accordance with aspects of this invention the triggering action is caused by a registry point or points which are formed on the belt record.

In accordance with other aspects of the present invention, the first and second scanning conditions may be varied as best suits a particular sound recording and reproducing operation. Thus, the first condition may be a gradual transverse motion of the scanning head and the second condition may be a cessation of the motion, or the first condition may be the absence of any scanning motion, and the second condition may be a slow or rapid transverse motion, or the first and second conditions may include various rates of transverse scanning motion, as

' explained hereinafter.

It is an advantage of the present invention that the synchronization of the motion of the transducer head 4 with respect to the motion of the record surface is attained simply and positively. Moreover, this synchronization may be attained without the need for alteration of the basic structures used in many conventional belt-record type sound recording or reproducing machines.

These and other objects, aspects, and advantages of the present invention will be in part pointed out and in part apparent from the following description taken in conjunction iwth the accompanying drawings, in which:

FIGURE 1 is a partial perspective view of a dual mandrel type of magnetic belt-record machine embodying the present invention;

FIGURE 2 is an enlarged cross sectional view taken along the line 22 in FIGURE 1 and showing details of a feed screw clutch and electromagnetic control solenoid therefor;

FIGURE 3 schematically shows an electrical circuit for operating the clutch control solenoid;

FIGURE 4 is a partial perspective view of a sound recording or reproducing machine embodying the present invention and using a relatively long, wide belt record which is folded for storage during use of the machine;

FIGURE 5 is an enlarged cross sectional view taken along the line 5-5 in FIGURE 4 and showing details of an electromagnetic clutch drive unit;

FIGURE 6 schematically illustrates an electrical circuit for operating this clutch drive unit;

FIGURE 7 diagrammatically illustrates a belt record with a sound track indicated thereon of the type made by the machine of FIGURE 1, some of the dimensions being greatly distorted for purposes of better illustration and-clearer explanation;

FIGURE 8 is a diagrammatic illustration of a part of a long belt record with a sound track indicated thereon of the type made by the machine of FIGURE 4, some of the dimensions being distorted for purposes of illustration;

FIGURE 9 is an enlarged sectional view through the margin of a record and through an associated electrical contact, taken along the line 9-9 in FIGURE 11;

FIGURE 10 is a schematic circuit diagram of a modified circuit arrangement for use with the machine of FIGURE 1 and corresponding in certain respects to FIGURE 3,, but producing an initial automatic phasing of the record and feedscrew;

FIGURE 11 is a cross sectional view of the record 10 and of the feedscrew 32 taken along the line 11-11 in FIGURE 1, looking toward the rear face of the gear 38, but with the indexing band 76 shown bridging the contacts 78;

FIGURE 12 shows a cross-sectional view of another embodiment of the invention in a dual mandrel machine similar to the machine shown in FIGURE 1;

FIGURE 13 is an enlarged sectional view of the modified clutch control circuit of the machine of FIGURE 12;

FIGURE 14 shows the electrical control circuit for the machine of FIGURE 12; and

FIGURE 15 diagrammatically illustrates a belt record with a partial sound track thereon as made by the method and apparatus of FIGURES 12, 13, and 14, some of the dimensions being greatly distorted for purposes of better illustration and clearer explanation.

Referring to the drawings in greater detail, FIGURE 1 shows portions of the record drive mechanism, feed screw drive mechanism, and the transducer head carriage of a dual mandrel type of machine using a magnetic belt record 10. In removing the record from this machine one mandrel, generally indicated at 12, supported on an axle 14 may be moved inwardly toward the other mandrel 16, supported on an axle 18, so as to reduce tension on the belt to facilitate its loading and unloading. The belt record is loaded by sliding it simultaneously over the rounded ends 19 (only one is shown) of these mandrels until its margin 20 strikes the flanges 22 and 24 on the adjacent ends of the mandrels 12 and 16, respectively,

and when the record reaches its fully loaded position against the flanges, as shown, the mandrel 12, which is spring biased outwardly, is released to apply tension to the record.

During sound recording or reproducing, the record is driven along its path around the two mandrels in the direction of the arrow 26 by a suitable drive mechanism including an electric motor, as is known in the art, which operates through an intermediate belt or gear drive mechanism (not shown) to rotate the axle 18 of the drive mandrel 16 in the same direction as the arrow 26. In order to maintain the record margin 20 firmly aligned against the flanges 22 and 24 during recording or reproducing operation, the axle 14 is canted slightly with respect to the axle 18 to provide a slight relative component of motion tending to drive the record continuously toward the flanges by suitable canting mechanism, such as disclosed in US. Patent No. 2,371,116 to Yerkovich, issued March 6, 1945. The record is driven by the frictional engagement of its undersurface with the relatively smooth cylindrical surface of the drive mandrel 16 or it may be driven by both mandrels. depending upon the machine construction. It moves past the record-engaging pole faces (not shown) of a magnetic recording and/ or reproducing head 28 mounted in a carriage 30.

Thus, with this frictional drive the record may slip or creep on the surface of the drive mandrel, or when the record becomes stretched as by the factors mentioned above,.it tends to revolve past the mandrel 16 at a ditlerent speed than it should. Therefore, if the feedscrew 32, which is driven by the same main drive mechanism (not shown) as the mandrel 12, were rotated continuously as in conventional machines the head might soon get out of phase with the sound track, as explained above.

In the methods and apparatus of the present invention this phasing problem is overcome, for the transducer head scanning motion is controlled by the motion of the record, and synchronized therewith. In this method the transverse scanning is continued in a first condition of operation until it is changed into a second condition of operation by the drive mechanism, and it continues in this second condition or" operation until triggered back into the first condition of operation by the record belt itself when the belt reaches predetermined positions in its path. This cycle of operation is repetitive, and may repeat itself at fixed intervals or during intervals of variable length, and these two conditions of operation follow each other in succession as the recording or reproducing takes place.

An embodiment of this method of synchronization of the scanning of the head 28 relative to the record 10, will be understood by considering the apparatus shown in FIGURES l, 2, 3, 7, 9 and 11. In the machine shown in FIGURE 1 during recording the combined revolution of the record 10 and motion of the head 28 produces a continuous magnetic sound track 33 (see FIGURE 7) on the surface of the magnetic belt record It In order to prevent the phasing problem discussed above, the head 28 is driven by intermittent rotation of the feedscrew 32. The feedscrew is rotated in the direction of the arrow 34 to slide the carriage along a guide rod 36 in a direction away from the record margin 25, so that the head 28 intermittently recedes from this margin while the record continuously revolves in the direction of the arrow 26. The magnetic sound track 33 is invisible, consisting only of a very thin narrow band (shown diagrammatically enlarged and shaded) of successive areas of varying intensity of magnetization corresponding to the variations of the sound being recorded, with narrow spaces 35, which may be considered barrier zones, between adjacent loops of the track. This recording operation straight adjacent the leading margin 20 of the record. It is intermittently moved away therefrom by the feedscrew 32. T he feedscrew is intermittently rotated by a gear ring 38 engaging a drive gear 46 (partly shown) which is driven by the same driving mechanism as the axle 18. Because it is driven by the same driving mechanism the feedscrew when it rotates, moves at a fixed rate relative to the mandrel 16.

In order to provide intermittent operation of the feedscrew, the ring gear 3% (see also FIGURE 2) is mounted to rotate fireely on the reduced end portion 42 of the feedscrew shaft, these parts being included in la feedscrew control clutch unit, generally indicated at M. A spider spring 46 carried on the reduced shafit portion 42 and thrusting against a shaft shoulder 4-8 biases ring gear 33 to bear against a clutch disc 59, which is threaded by a left hand thread onto the end of the feedscrew shaft 32 land is held in place by a lock nut 52. Hence, when the drive motor is energized, the driving face 54 of the ring gear 33, bearing against the annular lip on the disc 55 tends to rotate the feedscrew.

In order to allow the record belt It to control the condition of operation of the scanning, the clutch unit 44 includes a dog or deten't 56 on the end of a bell crank attached to an armature so. The armature is biased by a spring 62, in a counterclockwise direction around its pivot 6 so as normally to hold the dog 56 against the outer surface 66 of the disc so, whereby the dog so can abut against a stop 68 formed by the edge of a recess 7d in the surface of the clutch disc 5%}, as shown (see also FIGURE 2). When the detent as abuts against the stop 63, the rotation of the feedscrew is prevented, and the driving face 54 of the ring gear 38 slips against the disc 55d, thus putting the scanning operation into its second condition. In this second condition of operation which occurs in region (II) indicated in FIGURE 7, the feedscrew 32 is held stationary by the detent 56, and the record belt It? continues to revolve. Thus, the head 28 follows segments 72 of the sound track 33 thereon.

As will be explained later, the record controls the triggering of the scanning from this second conditionot operation back into the first condition, which occurs in the remaining region (I) indicated in FIGURE 7. In region (I) the feedscrew is allowed to turn, and the head 23 follows inclined or helical portions 74 of the sound tnack 33. The return to the second condition of operation is automatically caused by the drive mechanism when the detent 56 abuts against the recess stop 68 (after a full rotation of the feedscrew. As these conditions follow in succession, the intermittent helical path having straight seg ments at intervals as shown in FIGURE 7 is produced.

The helical paths 7 continue around the record Ill, as shown bytheir center line 755. This center line is dotted at 75', which represents the continuation of the helical tracks on the other side of the belt record. The relative dimensions of the record It? and of the sound track 33 are diagrammatically distorted for purposes of clearly explaining the invention. Thus, for example, the

'Width of the record and the Width of the sound track and of the butter zones 35 between adjacent turns have been shown greatly increased. In a typical application of the invention on a dictating I112....1ll'16 using a magnetic record there may be firorn 25 to 200 loops per inch of width of the record, that is, of the order of magnitude of a hundred lines per inch. The spaces between adjacent lines may be anywhere in the range of 3 times to of the width of the track, that is, of the order of magnitude of /2 of a track width.

In order to allow the record belt to trigger the scanning from the second into the first condition of operation, a control point or points are placed on the belt. In the embodiment shown, this control point is a small stripe "7'5 (FIGURES l, 3, and 7) of electrically conductive paint applied across the underside oi the belt It This stripe c arges? periodic-ally. closes an electrical control circuit between .a pair of electrical contacts 78 (see also FIGURES 9 and By closing the circuit between these contacts 7S, a solenoid 80 in the clutch unit 44 is energized drawing the armature 69 toward the end 82 of the magnetic core of the solenoid until a silencing felt bumper 84 strikes the solenoid 80. This motion of the armature lifts the dog 56 out of engagement with the recess stop 68, allowing the ring gear 38 to start turning the feed screw, thus commencing the first scanning condition. Soon after the feedscrew starts turning, the armature is released so that the dog 56 can slide along the face of the disc 58 ready to drop into the recess '79, once again to throw the scanning into its second condition of operation in which the feedscrew is held stationary.

Instead of a conductive paint mark, the control point or points used on the belt may be in the form of a notch or hole in the belt used with a pair of opposing contacts, allowing them to close against each other, or allowing one of them to contact the surface of a metal anvil to complete a circuit, or the control point may be a spot of colored paint to trigger a photoelecetric cell, or a magnetically recorded tone signal. However, I have found the conductive stripe 76 to be satisfactory and to lend itself to simplified circuit arrangements. The record belt may be made from plastic which is extruded as a long cylinder and may conveniently have the paint strip 76 continuously applied on the inside during this extrusion, the individual belt records being subsequently cut from the extruded cylinder.

Preferably, the record belt 16 and all other record belts for the dual mandrel machine contain an indication to the user that one edge is to be used as the leading edge to be inserted into the machine first. This indication may comprise a marginally printed indication 8-6 such as an arrow or This edge in. on the left margin 20 of the record. In normal usage, the machine is loaded with this indicate 86 toward the flanges 22 and 24.

The stripe extending clear across the inside surface of the record allows for an improper loading operation, which may occur through haste or inadvertence, in which the wrong edge of the record is inserted first. When only a spot or notch is used on the margin 29, a spot or notch (not shown) corresponding in position to this first spot or notch, is applied to the opposite margin so that the machine will operate even with the record reversed.

The number of control points 76 which are used depends upon the chosen value of the predetermined amount of belt travel which occurs during the first and second transverse scanning conditions, i.e. upon the number of triggering operations per record revolution (or upon the number of record revolutions for each triggering operation).

As discussed above, the predetermined amount of belt travel may be one complete record revolution, in which case the first and second scanning conditions each occur once per record revolution. Or the predetermined amount may be less than or more than one record revolution or may be a random amount, as explained hereinafter. As explained above, the first condition of operation (I) continues until the drive mechanism automatically places the scanning into its second condition (II). This first condition (I) continues for a first portion of this predetermined amount of record travel, and the second condition continues for the remaining portion of this predetermined amount of record travel. The triggering action only occurs once at the end of the predetermined amount of record travel. Thus, for example,,if the predetermined amount of record revolution is chosen as one full revolution of the record, then the first condition (I) of operation may be chosen to continue for some portion, for example, such as approximately 95% of the full revolution, and the second condition (II) then continues for Cir the remaining 5% of the revolution; similar to the arrangement shown in FIGURE 7.

If the predetermined amount of revolution of the record is chosen as one-half of a full revolution, then the first condition of operation may be chosen to continue for some portion of that one-half, and the second condition will continue for the remaining portion of that one-half. It is important to understand that the predetermined amount may be a full revolution, a fraction of a full revolution, or more than a full revolution or a random amount of revolutions of the record and the two transverse scanning conditions of operation (I) and (II) continue in succession for portions of the record travel whose total equals this predetermined amount.

One control point is used on the belt where the preetermined amount equals a full revolution, as illustrated in FIGURE 1. Two equally-spaced control points are used where the triggering occurs after every one-half of a revolution, three for a third of a revolution, and so forth.

Where the predetermined amount equals more than a single revolution of the belt record, one or more control points are used depending upon the feedscrew ratio, described hereinafter.

As shown enlarged in FIGURE 9, the contacts 78 are mounted upon an insulating block 88 and are bent back over their terminal ends on the bottom of the block and inclinedso that the margin 20 of the record when inserted as shown by the arrow 89 can slide up over them without catching. Their bend provides a spring action so they bear up against the underside of the record when it is fully inserted so as to make good contact with the control point conductive stripe 75, completing the solenoid control circuit shown in FIGURE 3.

This circuit includes a gas-filled thyratron 99 of the cold cathode type, such as a 5823 tube, including a control grid 2 to which a positive voltage must be applied to fire the tube. The circuit is energized from a suitable sixty cycle A.C. source through the supply terminals 94.

When the contacts 78 are bridged by the conductive stripe 76,'the A.C. supply voltage is rectified by the selenium rectifier 96 and is applied across the grid return resistor 98 and through the current-limiting resistor 16a; to fire the tube, allowing current to flow from its plate 162 to the cathode 104. A surge of current flows through the solenoid coil as, pulling the dog 56 out of engagement with the recess stop 68. A resistor Hi6 and condenser 108 are added in series across the solenoid in order to improve its operation.

Since AC. is used to energize the tube Ml, it automatically is extinguished when the plate voltage swings negative during alternate half-cycles and is re-fired during the next half cycle only if the contacts are still bridged by the conductive mark 76. I have found that it is preferable to have the control strip 76 sufficiently wide to bridge the contact 78 for at least second to insure that the disk 50 begins to rotate a sufficient amount so that the stop 68 will clear the 'dog 56 before the armautre (it? is released.

An advantage of using the cold cathode thyratron 943 is its instantaneous readiness for use, no delay for warm up. Also, such tubes are readily triggered in spite of any high contact resistance which may occur in the grid circuit, thus allowing the use of conductive paint and light spring pressure of the contacts 78 so that the conductive paint is a not unduly worn.

In the dual mandrel type of machine illustrated, the

ffeedscrew 32 is driven at a rate which is suificiently fast to insure that the first condition of operation (I) always is completed and the dog 56 has been allowed to hold the feedscrew in the second condition (II) for at least some period of time before the belt record has advanced its predetermined amount e.g. in the embodiment just described, before' one full revolution of the record has taken place. This fastfeed ratio is necessary to accommodate allranges of possible slippage and tolerance variations,

including short records and oversize mandrels, which result in a higher-than-average rate of record travel. In a particular embodiment of this invention the feed ratio between the feedscrew and drive mandrel are such that on the average the feedscrew makes one complete revolution, condition (I), while the record makes about 97% of a revolution. Variations in the amount of record travel are accommodated by the length of the second condition of operation (11), i.e. by the relative lengths of the straight segments '72 between straight line starting points A and finishing points B. These straight segments '72 are of indeterminate length depending upon how much creepage and effects from relative dimensions of record mandrels has occurred during the preceding condition (1). These straight segments continue until the next control point is reached on the record. Hence, as shown in FIG- URE 7, the ends B of the straight line segments 72 all occur at the same longitudinal place on the record determined by the position of the conductive stripe 76, but the positions at the beginnings A of the straight segments 72 depend upon all of the variable factors described above and hence may occur at different longitudinal positions on the belt record at each revolution, as indicated in FIGURE 7.

Since the scanning opeartion is repeatedly synchronized with the motion of the record after predetermined amounts of record travel, it is clear that the cumulative errors discussed above are eliminated. The scanning is placed in synchronism with the record each time a control point on the record triggers the scanning mechanism.

In a particular embodiment of this invention utilizing the dual mandrel type :of record drive arrangement, as shown in FIGURE 1, the following particular dimensions and speeds were successfully used. The record was a paper web material coated on its outer surface with a layer of magnetic material, and it was 3 /2 inches wide and 12 inches around. The mandrels were each 1.75 inches in diameter, and the drive mandrel was rotated at a speed of approximately 36 r.p.rn., to provide a record speed of 3 inches per second or 15 feet per minute, being equivalent to an average record speed of 15 r.p.m. The feedscrew was rotated at slightly more than 15 rpm. and had a pitch of 52 threads per inch, thus providing 52 sound tracks per inch on the surface of the record, giving a sound track pitch of .91923 inch per record revolution and giving a total recording time of 12 minutes. On an a erage, as mentioned above, the head was scanned at its first rate during a first portion of a full revolution amounting to approximately 97% and on the average remained stationary during the remaining 3%. The sound track was .014 inch in width and the average width of the intermediate bufier zones 35 was .00523 inch, being a little more than /3 of the track Width.

Another embodiment of my invention will be understood by considering FIGURES 4, 5, 6 and 8 using the same method, but having different operational relationships from those described in connection with the first embodiment.

This machine is a type of machine as described more fully in the copending application of Edward S. Gillette et al., for Folded Belt Record Machine, filed June 18, 1954, Serial No. 437,829, now Patent No. 2,865,639, which uses a relatively long loop of a wide, folded-type of belt record 12%, partially shown. The main bulk of the record is stored below the scanning mechanism in a container (not shown) with the record folded back and forth upon itself in the manner of the folds in an accordion, causing creases 121. During operation the record is peeled off from the bottom of the storage pile and-pulled up in the direction of arrow 12.2, passing over a freely rotatable supporting drum 124 under a transducer head iiadand on down between a drive roller 128 and a presser roller lfitl which holds only the center of the belt against the drive roller to insure that the record id is pulled straight, as explained in greater detail in the above copending application.

This folded-record type of machine is designed for the continuous recording of sound over long periods of time, such as from four to twenty-four hours per record, to be used for example, at airports to obtain a continuous record of the conversations via radio between the control tower operator and the pilots.

A suitable drive mechanism powered by an electric motor (not shown), as described in the above copending application, rotates the drive roll-er 123 and also drives a feedscrew 132 intermittently to feed the head 126 away from the margin 134. (see FIGURE 8) over the surface of the record.

The drive to the feedscrew from the main driving mechanism passes through an electromagnetic drive corn t-rol clutch unit, genenallyindicated .at 136. The drive can be traced as follows: a gear 133 (shown broken away) is driven from the main drive mechanism (not shown) by suitable gear train from the drive motor shown in the above copending application and is used to drive a clutch gear 34% (see also FTGURE 5) mounted by a collar 142 to rotate freely on a stub shaft 144 projecting from the machine frame 1 6. The gear 14-h is arranged to engage a freely rotatable clutch disc 1 53 when a pair of solenoids 153 and 151 are energized and pull the clutch disc over to the dotted-line driving position 154 shown in FIG- URE 5. The solenoid pole tips 152 and 1.53 are spaced to clear the clutch disc 14-8 when it is in driving position 154. A compression spring 156 carried in a recess 158 in the collar 142 normally holds the clutch disc out against a retaining clip spring 15% on the outer end of the stub shaft. Fastened to the outer side of the clutch disc is a gear 162 which drives the feedscrew gear 1dr: through an idler 164.

As in the first embodiment, this apparatus has two conditions of scanning. During the first condition of operation (l), as shown in FIGURE 8, the head 1% is moved laterally for a period of time amounting to 15 inches of record travel, thus following short helical paths 1.63 over the surface of the record 12%, and during the second condition of scanning (ii) the head remains stationary, so that the remaining portions of the sound track 33 follow long straight line segments 172 parallel to the edge of the record. It is to be understood that FlGUl-KE 8 represents only a small fraction of the whole belt record 12%, being that part which includes the control point 17 and the helical path portions 163. These helical paths 168 may continue for only about 15 inches of belt travel, while the straight line segments 172 continue for the remainder of each revolution and extend the length of the whole rest of the record 12ft, not shown in FIGURE 8 to simplify the drawings. That is, each of the tracks 17 leaving the bottom of FIGURE 8 at 173 passes around the rest of the record belt and returns at 173 The recording or reproducing head 126 depends from a carriage 17d slidingly mounted on a guide rod 17% so as to move parallel with the surface of the drum 1% over which the record moves.

In this embodiment of the invention the predetermined amount of belt travel is shown as one complete revolution of the record belt, and hence a single control point 1'78 is used, comprising a rectangular spot of conductive paint applied to the underside of the margin 134;. As explained above, a corresponding spot 186 (FIG- URE 4) may be used under the other margin in case the folded record is inserted in reverse, or a conductive stripe extending the width of the record undersurface may be used.

Referring to the control circuit shown in FTGURE 6, when the control point 178 bridges a pair of contacts 182, a circuit is completed which fires a thyratron 13d and energizes the solenoid coils 15d and 151. A pair of supply terminals 1% for this circuit, which is designed for use with a DC. source, are suitably energized, as from of fluctuations at the terminals 186, which constant voltage is fed through a resistor 192 to the starting electrode 194 of the tube 184. This voltage is arranged to be below that necessary to fire this tube. The regulated voltage from tube 1% also charges a condenser 196 through the resistor 192 and a resistor 1 3 connected to the negative side of the line.

When the contacts 182 are bridged by the control point 178, the voltage across the neon tube 19% is added to the voltage across the condenser, firing the thyratron 184 and allowing current to how from the plate 204) to the cathode 292. The relay 2% is energized through a current limiting resistor 2%, closing relay contacts 268 and completing a circuit through the two solenoid windings 158 and 151 in series to attract the clutch disc 14%. Thus, the machine is placed in its first scanning condition (I); the feedscrew is rotated, and the head 1Z6 follows the diagonal or helical paths 168.

Since direct current is used to energize the tube 184, it continues to conduct until its circuit is broken by a cathode-circuit switch 219 operated by a cam 212 with a recess 214 and a co-operating follower 2i The follower 216 normally bottoms in the recess 21.4- allowing the cathode circuit switch 21% to be closed. When the thyratron 184 is fired by the control point 178, the clutch disc 143 starts to turn the feedscrew and cam so that the follower Zl rises up out of the recess 214 into the position shown in FIGURE 4. Thus, the switch 229 is opened and the thyratron is extinguished; however, at the same or a slightly previous time a switch 218 is closed, completing a circuit from positive terminal iefi directly through switch 213 and the solenoids d and 151 to the other terminal 186, thus maintaining energization of the clutch solenoids. The feedscrew continues to turn until the follower 216 drops into the recess, at which time the cathode circuit is again closed, and the solenoids are deenergized by the switch 215, stopping the feedscrew and placing the machine in its second condition of scan (II) with the head following one of the long straight paths 172. The thyratron will not fire until a control point 178 is again reached, repeating the cycle of operations.

From the above description it is seen that the travel of the record belt is divided into predetermined amounts and that the scanning mechanism is synchronized with the record at the commencement of each of these amounts, thus the cumulative errors discussed above are eliminated.

In a particular embodiment of the folded-record type machine, the machine would provide up to 24 hours of continuous recording, depending upon the length of the folded record and upon the way in which the folded portion was stored, as described in the above copending application. In order to provide four hours of continuous recording, the record was a paper web coated by magnetic material, 3 /2 inches wide and 34 feet long, in a closed loop, consisting of 48 folds each 8 /2 inches long. This record was driven at 3 inches per second or 15 feet per minute, with the feedscrew being rotated once during the initial period of each revolution of the belt record. The rotation of the feedscrew took five seconds, which amounts to 15 inches of record travel. The feedscrew had a pitch of approximately 40 threads per inch to provide a total of 135 sound track loops on the record with a pitch of .025 inch and a track width of .014 inch, leaving a barrier of .011 inch between adjacent tracks, almost equal to the width of the track itself.

In FIGURE 3 is shown an A.C. circuit and FIGURE 6 shows a D.C. circuit. Either of these circuits may be adapted for use with either type of machine. Thus, in order to use the circuit of FIGURE 3 to perform the functions of the circuit of FlGURE 6, the solenoid 33 may be replaced by a relay similar to the relay 204 but with an extra pair of contacts to provide a self-holding circuit, as is known in the art. This relay in turn would energize the solenoids i5} and 152. The releasing switch 216 would be placed in the self-holding circuit of the relay, thus interrupting the feedscrew drive at the appropriate time.

To adapt the circuit of FIGURE 6 to perform the functions of the circuit of FIGURE 3, the relay 204- is replaced by a solenoid and pivoted armature arrangement similar to that shown in FIGURE 3, and a cam disc is oriented on the feedscrew 32 in position to open the contacts 21% in time for the armature detent to arrest the feedscrew.

FIGURES 10 and 11 considered with FIGURES 7 and 9 show a modified automatic record phasing arrangement corresponding in certain respects to the arrangement of FIGURES l, 2, 3, and 7 and 9. Components in the circult of FIGURE 10 performing cor-responding functions to those in the circuit of FIGURE 3 are marked with the same reference numerals, followed by a distinguishing sufiix. The purpose of this modified arrangement is automatically to return or index the feedscrew 32 (FIGURE 11) whenever a record it? is unloaded from the machine, to an initial position corresponding to the point of transition from the first to the second conditions of operation, i.e. to the position wherein the dog 56a (FIGURE 10) drops into the recess and abuts against the stop 63a. Thus, when a record with previously recorded material is again loaded for reproduction, it is automatically in phase from the very initial part of the sound track. Also, advantageously a blank record has its sound track start without an unduly long straight initial portion, such as portion '72 shown in FIGURE 7.

With the circuit of FIGURE 3, the feedscrew 32 is left in a random position following unloading of a record, and hence when a record with recorded material thereon or a blank record is loaded into it, the head may be out of phase with the desired track for some random amount of the first record revolution, i.e. until the contacts 78 have been bridged and have triggered the scanning operation for the first time. This unphased initial period may amount to almost a full revolution of the record, requiring 4 seconds in the particular dual mandrel machine described above, but the modified circuit of FIGURE 10 does away with this initial random period. t

In the circuit of'FlGURE 10, assume that the operator has finished recording and desires to eject a record. The first step is to move the carriage 30 to its initial position near the flanges 22 and 24 as required by an interlock arrangement, as is known in the art, which prevents ejection of the record until the carriage is in this position. Assuming that the dog 56a does not happen to be in the recess 76a, which is the desired initial position of the feedscrew, then when the record 10a is unloaded by using a record ejection lever mechanism on the front of the machine (not shown), the idler mandrel 12 is moved inwardly, as described above, and a lever (not shown) on its shaft 14 operates a first and second single pole double throw switch 226 and 222, respectively, shown ganged together, to move the switches into their lower positions, as shown. The first switch 220 completes a circuit from one of the .power terminals 94a through a rectifier 224, across a filter condenser 226, through a drive clutch control solenoid 228, and through switch 22%) and lead 221 to the other power terminal. This completed circuit energizes the clutch solenoid in order to provide a drive connection from the main drive motor 236 to the drive gear 40 (FIGURE 1). The stopstart operation of the machine shown in FIGURE 1 is controlled by means of the clutch solenoid 228, as is known in the art, which must be energized to prov d a drive. During normal use, the switch 220 is open, and a hand or foot switch 232 is used to control the drive solenoid 228. Y

The switch 222 serves to by-pass a cradle switch. 234,

which normally de-energizes the motor 236 whenever the hand microphone unit (not shown) is hung up, as known in the art. This switch 222 completes a circuit to an indexing switch 236 (see also FIGURE 1) carried on th carriage 3t), and which is now adjacent the ring gear 3% because during the first step of record ejection the carriage was manually shifted there. Thus, the push button 233 of the index switch lies in the path of an index switch actuator arm 24) (see FIGURE ll) which has an end secured to a pivot 242 and is biased by a spring 244 to ride against a cam 246 located on the feedscrew 32 closely adjacent the ring gear 38. An elevation 2 28 on the cam 245 is oriented with respect to the recess stop 68, shown in phantom, so that the actuator arm Mill is raised at the same time as the dog 56 drops into the recess stop 68. A sloping surface 250 on the free end of the arm 24% pushes the button 23% inwardly as the arm is raised, thus opening the switch 236 and stopping all further action leaving the feedscrew in its desired initial position with the dog 56 in the recess. Therefore, the feedscrew is always left in the same position after record ejection, regardless of whether the hand microphone was hung up immediately following record ejection or whether the manual control switch 232 was released too soon.

An advantage of this arrangement is that during normal operation the carriage and index switch 236 are spaced away from the arm 24% and no operation of the switch occurs, with rotation of the feedscrew, thus greatly reducing wear.

When a machine is equipped with the modification of the circuit shown in FIGURE 10, it is preferable that the user always insert the record belt l-J'a in the same relative position so that the sound tracks start initially in proper orientation with respect to the feedscrew and head, i.e. start in phase. An arrow 219 or some indication 86 (see FIGURE 1), such as a trademark is placed on the top side of the leading margin of the record. This mark serves two functions. It tells the user which edge is to be inserted first, or last (as the case may be) and allows the user to align this mark on the record with a fixed mark or position on the frame of the machine so that every record always has substantially the same initial position and the feedscrew has the same initial position. The relative orientations of the control point 76b and the loading indication 219 are such that when the machine is initially started following loading, the record will travel approximately only 2 or 3 inches before the point 76a reaches the firing contacts. This 2 or 3 inches provides sufficient latitude in positioning the record, so that the loadin position of the record is not very critical.

With this arrangement, since the head is always started in the same initial position, and since the belt record is always started in the same position,'the head is in phase from the first instant of operation.

In the transcribing machine, the relative initial position of the head is adjusted at the factory so that the record must make at least one full revolution before the beginning of the sound tracks are reached, and thus the head always starts reproducing in phase with the sound track even though the transcribing machine omits the initial indexing arrangement shown in FIGURES 1, l and 11.

Considering again briefly the first embodiment described, it will be understood that the switch 236, arm 240 and cam 246 would be omitted from the machine in the first embodiment, these being used in conjunction with the circuit of FIGURE to produce indexing of the feedscrew always to the same initial position, each time a record is loaded into the machine.

Another embodiment of my invention, in which the predetermined amount of record travel is random and normally amounts to more than a full record revolution, will be understood by considering FIGURES 12, 13, 14, and in conjunction with FIGURE 1. This embodiment uses the same methods as the other embodiments, but it is explained last because the concepts involved are somewhat more difficult to understand. Thus, the preceding explanation serves as a foundation for the explanation of this embodiment. This embodiment is preferable for certain applications because, on the average, the triggering action occurs only once for each three or four revolutions of the record, resulting in longer life of the operating parts. The triggering may occur more often where the cumulative error is abnormally large, as might result from the accidental presence of a lubricating agent on the surface of the drive roller, e.g. wax or graphite particles, or where the record has stretched.

In FEGURES 13 and 14 elements performing functions corresponding to those of elements in other figures have the same reference numeral followed by an appropriate suffix.

in this embodiment a clutch control unit 268, FIGURE 13, is used in order periodically to interrupt the drive to the feedscrew. The drive can be traced from the drive gear to a ring gear 38b which rotates on an end portion 4% of the feedscrew 32b and thence through a clutch pin 263 projecting from a face of a clutch disk 26 which is spline-d at 26s to the feedscrew end 42b. When a clutch solenoid 258 is tie-energized, a compression spring 276 thrusting against a washer 272 fastened to the feedscrew end, biases the clutch disk toward the right so that pin 262 engages the side of ring gear 381'). This pin then enters whichever one of the oblong holes 274 (FIGURE 22) in ring gear 331; with which it coincides, completing the drive linkage.

The solenoid 268 is advantageously arranged to have a central pole 276 juxtaposed with the end of the feedscrew shaft and an annular pole 278 near the side of the clutch disk 264. Thus, the feedscrew end 42b acts as a portion of the magnetic circuit to increase the attraction between the annular pole 2'73 and the clutch disk 2&4.

Energization of the solenoid 268 pulls the disk 26% to the left, to the phantom-line position shown in FIGURE 13, withdrawing the pin 262 from the hole 274 with which it was engaged, breaking the drive to the feedscrew and allowing it to stop.

The circuit of FIGURE 14 is used to control the energization of the solenoid 268, and includes a pair of triggering contacts '78 riding against the undersurface of the record it? and a normally-open, cam actuated switch 2%. In order to tire thyratron tube 9%!) to energize the solenoid Zed, the contacts '73 must be bridged by the conductive index point 7% on the record while the switch 23% is momentarily held closed by a raised cam 282 on the periphery of the clutch disk 26 3, which acts through a camfollower 2554.

Thus, during operation the record is revolved and the feedscrew is rotated, producing a sound track on record 1 3 having an initial helical path portion 286 (see FIGURE 15) during a first condition of operation, but whenever the record has drifted back relative to the feedscrew sufficiently far for a coincidence to occur in the bridging of contacts '78 and in the closure of switch 286, then the machine is triggered into its second condition of operation in which the ieedscrew is stationary. The solenoid 263 is energized, momentarily pulling pin 262 from one of the holes in ring gear 385, stopping the feedscrew and allowing gear 28:) to continue rotating freely on shaft 4 1;. Buring this second condition a straight portion 288 of the sound track is formed, for the record continues revolving while the feedscrew is at rest. As soon as the conductive mark 76 has moved beyond a position to bridge the contacts 7%, the firing circuit to the control grid d2]; is broken, and the tube 9% ceases to conduct, de-energizing the solenoid 268. Clutch disk 2.64 is then moved by spring 27% back to the right, and when ring gear 33b has been rotated an amount determined by the spacing of the holes 2%, which here is approximately 60, the pin 2%2 slides into the next hole 27'4 and the machine is again in its first scanning condition, forming the next helical portion 236 of the sound track. This cycle repeats itself,

but the length of each cycle of operation is a random number of integral record revolutions.

In FIGURE 12, as shown, the pin 262 has just slipped into a hole 274, indicating that the machine has just completed its second condition of operation, in which (while the feedscrew was stationary) the record has advanced an amount corresponding to the amount it normally advances during 60 of feedscrew rotation, i.e. about ,6 or 17% of a record revolution. Thus, during this approximate 17% of a record revolution, the control point of conductive point 76 has moved past contacts 78 to some position such as shown in phantom at 298 before the feedscrew again begins turning. During the next rotation of the clutch disk 264 and of the feedscrew, the record does not quite complete a full revolution and so the control point is at position 350 when the cam 232 again raises its follower. The reason that the record drops behind is twofold; first because the many factors which are discussed above tend to cause the record to slip or drift so asvto revolve slower than would be expected from the surface speed of the drive mandrel, and second because of the slightly increased feedscrew speed, discussed below. During successive rotations of the feedscrew the control point 76 occupies positions such as indicated in phantom at 302, 394 and when it has dropped back again to the firing contacts 78, the tube 96b is again fired.

As shown diagrammatically in FIGURE 12, the main drive motor 2% drives the mandrel 12 through a coupling arrangement 292 and also drives the drive gear 4% through a coupling arrangement 294, which may include a feedscrew speed regulation unit such as a gear box 296. In this machine the feedscrew is arranged, when it turns, to turn at a slightly increased speed. Thus, for example, in this machine where the record is revolving at 15 rpm. the feedscrew, when it rotates, is rotated at a speed in the range from 2% to faster than would be used in a similar type of machine with the same sound track dimensions and space between adjacent tracks. In this machine I prefer to run the feedscrew at a rate of 16 or 17 rpm. instead of the usual 15 rpm, e.g. about 6% or 7% faster. The feedscrew is'run at this slightly faster rate for two reasons: first, so that on the cumulative average, including those periods during the second conditions of operation when it is stationary, it is making about the same number of rotations per record as in a conventional machine; so that the same total number of revolutions of sound track are obtained. Second, the feedscrew must be sufficiently fast to accommodate any unusually fast record, i.e. as with an oversized mandrel and an undersized belt. If the record goes faster than average, the result is that the first conditions of operation include more revolutions of record.

In the diagrammatic representation of a record shown in FIGURE 15, the heavy dash and dot line 3% represents a continuous helix. line of a sound track which would result if the record were used on a machine having a feedscrew speed such as 15 rpm. and assuming that the record were driven at a steady 15 rpm. with a pitch of 52 lines per inch. The actual sound track is shown as having a width be tween its side edges 398 of about .014 inch with a space between adjacent tracks in the range of about .002.008 inch, the average being .00523 inch. On the upper face of the record, as seen in the drawing, the centerline of the actual sound track is shown as a full line 310 mid-way between track edges 308. On-the reverse face of the record, for the sake of simplicity, only the actual centerline, 310' (shown dashed) and the theoretical helix 3% are shown.

Some of the many results of the operation of this random length periodic phasing system can be seen by comparing the centerline 319 of an actual sound track with the theoretical helix 3%. The centerline 31G begins to the left of the theoretical helix 3% as seen at the left edge of record 16. During the first two revolutions of This is the theoretical centerthe record'the actual centerline gains on the theoretical helix, until at point D centerline 31% moves ahead, due to the slightly increased feedscrew speed discussed above. If the record were slipping badly, the centerline 316 would cross helix 3% sooner that two revolutions; if the record were faster, due to the fflCt discussid above, then centerline 31% might not cross the helix 366 until several record revolutions had occurred.

For approximately two revolutions more (making a total of about four revolutions for condition 1 during this cycle) centerline 31d progresses steadily ahead of helix 386. At E condition II begins, and the straight track portion 288 is formed, lasting for about /6 of a revolution. At F the track again begins as a helix, .and the machine is again in condition 1. During the straight track portion between transition regions E and F, the centerline 31% drops behind the true helix 3%, which crosses the centerline at G.

For purposes of better explanation it is assumed that during this second cycle of operations beginning at area F that the record It) is beginning to slip somewhat more than durim the first cycle. Thus, from region F the actual centerline 31d begins to overtake the helix 396 at a faster rate than during the first cycle. At point H at the completion of about one and a half revolutions, centerline 31d crosses helix line 395. In another approximate one and a half record revolutions, at position I the machine is again triggered into its second condition of operation. Once again, the actual centerline 310 of the sound track drops behind the helical line 396. At position K the machine again returns to its condition I and helical scanning occurs, and so forth during the opera- -tion.

Reviewing the first two cycles of operation, it is seen that the record revolved four times during the first cycle and three times during the second cycle. That is, the predetermined amount of record revolutions is random. Also, it is seen that condition 11 is always about the same amount of record revolution, because it occurs while the clutch plate is revolving the distance between two holes 274. Variations in the amount of record which pass the head while the machine is in condtion II may occur, but they are slight since condition II only takes about /5 of a record revolution, and the amount of variation in slippage which can occur and accumulate during this small fraction of a record revolution is small.

Condition I occupies the balance of each cycle. Each cycle '15 very nearly an integral number of record revolutrons for they all are initiated by the control point 76 on the record, the random number of record revolutions being controlled by the requirement that cam switch 280 must be closed at the same time that stripe 76 is bridging the contacts 78.

The cam 282 and the stripe 76 both have a consider able Width so that the exact position (such as position E) at which the machine is triggered from condition I to condition 11 may vary slightly rom cycle to cycle.

In order to prevent the machine from missing the initiation of any cycle, the effective sum of the widths of the cam 282 and the width of the stripe 76 must be sufficiently great that even a record with a large slip cannot drop backward during successive cycles so as to fail to trigger the tube 9%.

' It is possible to have more than one control point 76 on the record. For example, two evenly spaced conductive paint stripes may be used, in which case the predetermined amount of record revolution may be an integral number o f revolutions or a number of half revolutions. Three evenly spaced conductive paint stripes would give as the predetermined amount combinations of multiples of thirds of a revolution.

The result of any of these random phasing systems, as described above, is that when the record is slower than average, the tube 9% fires more often and vice versa when the record is faster than average. Thus, the center 17 line of the sound track is maintained at all times within or at the most 26% of its own width of a true helix over the entire width of the record. 7

Since the recorded track is automatically maintained on the average as a true helix over the entire record surface, the reproducing problem is greatly simplified. Thus, either of two kinds of reproducing or transcribing machines may be used. A machine without automatic phasing control may be used, in which case the reproducing head will follow a continuous helical path whose pitch may vary more or less from the true helix due to slippage, and the person operating the transcribing machine will have to phase it manually from thne to time. The amount of phasing required is considerably less than that which would be required if the sound track were not maintained as an average true helix.

Preferably the reproducing machine incorporates automatic phasing also. This might be of the fixed predetermined amount type or of the random predetermined amount type.

In the latter case the head is re-phased at random and caused to average the same true helix 3%. The reproducing head also may deviate 10% or from the true helix 306, but never more. Thus, the maximum possible deviation of the reproducing head from the track can never be more than somewhat less than the sum of the maximum recording and reproducing machine deviations, i.e. less than 40% of the Width of the track itself. This large deviation would happen only if the triggering of the phasing of the reproducer were occurring at other places on the record from those at which this triggering had occurred in the recorder.

Thus, wi h my invention, a random phasing action can also produce correct registry between the sound track and the reproducing head to provide good sound reproducing quality.

The advantages of this latter system are, that the triggering takes place less often, thus prolonging the life of the operating parts. Moreover, if for any reason the phasing system should fail, the result is merely to produce a continuous helix, so that the material being dictated would be recorded and not lost by having the head repeatedly retrace a circular path at the same spot on the record.

Thus, it will be seen that the methods and apparatus of this invention are well adapted to carry out the ends and objects hereinbefore set forth. Two embodiments of the invention have been described, and it is to be understood that they can be modified so as to best suit the needs or particular uses. It is to be understood that certain features of the invention can at times be used to advantage without a corresponding use of other features and, therefore, that the examples set forth above are for the purpose of teaching those familiar with this art the principles of the present invention and how to apply them for their particular uses, and they are not intended to be a definition of its scope or an exhaustive analysis of all of the possible forms or uses of this invention.

I claim:

1. The method of tracking a record head across a magnetic record which is adapted to have deposited thereon a plurality of side by side signal tracks lying along the direction of motion of the record relative to the head comprising the steps of moving the record at substantially constant velocity in a first direction relative to said record head, moving said record head slowly relative to said record in a second direction approximately at right angles to said first direction to trace out a signal track which is inclined at a slight angle to said first direction, periodically at equal intervals measuring the amount of travel of said record head relative to said record in said second direction, and if the cumulative error in the amount of travel of said record head relative to said record along said second direction does not exceed a predetermined value, then continuing the motions of said record and head in both said directions for the next one of said equal intervals but if said error exceeds said predetermined value, stopping the motion of said head relative to said record along said second direction without changing the relative motion in said first direction and then after a given interval resuming the relative motion in said second direction. I

2. In the art of recording and reproducing signals on a generally helical track having closely spaced turns on an endless belt record, the method for following within operating limits with a scanning pickup the actual signal track on the belt record without using the signal track itself to keep the pickup within said operating limits, said method including the steps of recording a signal on the record along a generally but intentionally not ex actly helical track which lies within 'a given limit of divergence from a theoretically perfect helical line on said record, and thereafter reproducing said signal by scanning the record with a pickup along a generally but intentionally not exactly helical track not necessarily the same as the actual signal track but which lies within another given limit of divergence from said theoretically perfect helical line, said limits of divergence being at least roughly of equal magnitude and separately and together being small enough so that the maximum divergence of the scanning pickup track from the actual signal track is not greater than that allowable for good signal reproduction and small enough so that the scanning pickup always overlaps at least onehalf the width of said signal track and does not overlap an adjacentturn of said track, whereby even though the length of the belt record may change slightly in the time between recording and reproducing, or even though the belt record may slip slightly on its drive mandrel during either operation, said scanning pickup will always follow Within operating limits of said signal track.

3. The method as in claim 2 in which an index mark on the belt record is utilized at intervals as a bench mark in keeping said tracks within said limits of said theoretically perfect helical line.

4. The method as in claim 2 in which as the belt record moves longitudinally past the scanning pickup the scanning pickup is moved transverse to the belt record at a speed faster than that needed to keep pace with said theoretically perfect helical line, whereby when said pickup moves beyond a limit of divergence from said perfect line, the pickup can be brought back within said limit by holding it from moving transverse to said belt record but without interrupting the motion of said record longitudinally past said pickup. V

5'. An overall method of synchronizing the travel of a transducer head across a short belt record to follow a groove-less generally helical signal track thereon comprising the steps of indexing the record relative to the head prior to recording, recording along a generally but not exactly helical track by moving the head slowly transverse to the record while it rotates past the head and at repeated short intervals brieily stopping the transverse movement of the head while the record continues to rotate, and then playing back the record by indexing it relative to the head in exactly the same position as with recording, moving the head generally at the same speed slowly transverse to the record While it rotates past the head and at repeated short intervals briefly stopping the tranverse movement of the head while the record continues to rotate.

References Cited by the Examiner UNITED STATES PATENTS Re. 23,112 5/49 Squire 179-1002 2,223,723 12/40 Fox 27417 (Qther references on following page) 1Q 25 UNITED STATES PATENTS' 2,550,803 5/51 Goddard 27441.4 2,253,568 8/41 La Forest 274 17 3 2,268,645 1/42 Dann 274-17 2 270 332 1 42 Dunning 5 N RTON ANSHER, Primary Examiner.

2,279,227 4/42 Dunning 274-17 STEPHEN W. CAPELLI, ANTONIO F. GUIDA, 2,371,116 3/ 45 Yerkovich 27411 Examiners. 

1. THE METHOD OF TRACKING A RECORD HEAD ACROSS A MAGNETIC RECORD WHICH IS ADAPTED TO HAVE DEPOSITED THEREON A PLURALITY OF SIDE BY SIDE SIGNAL TRACKS LYING ALONG THE DIRECTION OF MOTION OF THE RECORD RELATIVE TO THE HEAD COMPRISING THE STEPS OF MOVING THE RECORD AT SUBSTANTIALLY CONSTANT VELOCITY IN A FIRST DIRECTION RELATIVE TO SAID RECORD HEAD, MOVING SAID RECORD HEAD SLOWLY RELATIVE TO SAID RECORD IN A SECOND DIRECTION APPROXIMATELY AT RIGHT ANGLES TO SAID FIRST DIRECTION TO TRACE OUT A SIGNAL TRACK WHICH IS INCLINED AT A SLIGHT ANGLE TO SAID FIRST DIRECTION, PERIODICALLY AT EQUAL INTERVALS MEASURING THE AMOUNT OF TRAVEL OF SAID SECOND HEAD RELATIVE TO SAID RECORD IN SAID SECOND DIRECTION, AND IF THE CUMLATIVE ERROR IN THE AMOUNT OF TRAVEL OF SAID RECORD HEAD RELATIVE TO SAID RECORD ALONG SAID SECOND DIRECTION DOES NOT EXCEED A PREDETERMINED VALUE, THEN CONTUINING THE MOTIONS OF SAID RECORD AND HEAD IN BOTH SAID DIRECTIONS FOR THE NEXT ONE OF SAID EQUAL INTERVALS BUT IF SAID ERROR EXCEEDS SAID PREDETERMINED VALUE, STOPPING THE MOTION OF SAID HEAD RELATIVE TO SAID RECORD ALONG SAID SECOND DIRECTION WITHOUT CHANGING THE RELATIVE MOTION IN SAID FIRST DIRECTION AND THEN AFTER A GIVEN INTERVAL RESUMING THE RELATIVE MOTION IN SAID SECOND DIRECTION. 